Simply , you do not become ''pro'', you just start to use your mind and react quick that's all. ect. Don't get scared when a team fight starts or something that will start your adrenalin, Just be calm and think about what are the possibility's that you can do. Being calm and thinking will make you do something right for your team and for your self. Plus with a bunch of luck and quick reacting to whats happening will make you ''pro'' .

Yeah, that's why I'm asking. It's not that I'm really thinking of being a professional, but I was curious as to how actually pros became pros. What did they do to get paid, etc..? Just team up and win onlines and LANs?

Hi.
The difference between a good player and a bad player is consequence of many little particular aspects in game, like "last-hit" or "ward".
You can find everywhere a build of your main champion, so this is not a difference.
The pro player knows all of those aspects.
He knows all the skills of champion roster and for that he is able to predict enemies moves or which enemy attack first or which not attack.
Finally, the pro is able to use many champions in many roles at 100% power.
A Warwick played bad and a Warwick well-played (ex: combo Q-R-Ignite-Q-W).
Essentially, The Pro is a player who know how to do, when and why.
Ps: sorry for my bad english XD

There are several basic ways of getting paid:
1. winning cash prizes in tournaments (requires being better than the top teams in said tournaments consistently)
2. getting paid by a third party to appear in tournaments (I.E. getting sponsored)
3. streaming and getting money from streaming bodies based on ad revenue
4. selling memorabilia or your skills directly to your fan base (paid lessons, Elo boosting, et cetera).

Becoming a pro consists of
a. finding your revenue venue
b. working your way towards making that venue work
c. succeeding in (b).